Thermoplastic structural components and structures formed therefrom

ABSTRACT

Thermoplastic structural components utilized within building construction as permanent formwork. The components formed with openings along a length which serve to allow concrete to flow from one form to adjacent forms. Thus, filling the components forming a surrounding wall of a building. The openings allow for air circulation within components forming a roof assembly. The components are co-extruded with a protective skin along outer surfaces thereof. Grooves are provided along the length of the component for mating with interlocking flanges of a box connector. Planar spaced walls are provided within each component and have a series of openings along a length thereof.

FIELD OF THE INVENTION

This invention relates to reduction of the costs of the novelthermoplastic structural system and structural components therefor andbuilding structures erected therefrom which are disclosed in mycopending Canadian Application Ser. No. 2,070,079, filed May 29th, 1992without adversely affecting their integrity.

BACKGROUND OF THE INVENTION

The structural system disclosed in my said copending applicationcomprises novel interlocking thermoplastic structural components whichcan be mass produced at low cost and which can be quickly and easilyinterlocked together to erect a wide range of structures which willrequire minimal maintenance and will be safe from termites, corrosion,rust or rot and will be highly resistant to the effects of weathering.

The present invention is directed to significantly reducing the costs ofsuch components and hence the costs of structures erected therewithwithout sacrificing the structural integrity of the components orsystem.

Further the invention is directed to such cost reductions of thecomponents themselves and the structures formed therefrom withoutincreasing the costs of production of the components or interfering withthe ease of their assembly.

Further the invention is directed to providing such structuralcomponents as to aforesaid which will facilitate the conversion of thewalls erected therewith into permanent wall structures, will enhance theair circulation in roofs erected therewith, and will provide reducedthermal transfer between the exterior and interwall surfaces of thewalls and roofs.

DESCRIPTION OF PRIOR ART

While the use of plastic to form wall panels or the like for use inbuilding construction has been proposed, such panels have not had thenecessary load bearing or other structural requirements to formpractical structures which could be mass produced at low cost andquickly and easily assembled to erect durable low cost structures and,in particular, low cost housing.

U.S. Pat. No. 3,992,839, for instance, discloses a plastic panelfabricated from separate panel members, preferably formed of polyvinylchloride which snap together to form a thin wall panel. The panels inturn are formed to snap together to provide a wall structure. Suchfabricated panels are inherently weak and lack the strength and loadbearing capacity to form adequate structural components for use, forinstance, in the forming of the walls and roof of a practical durablebuilding.

U.S. Pat. No. 3,362,507 discloses the use of tongue and groovedindividually prefabricated panels said to be preferably of plastic whichare bonded or glued together and used particularly for the forming ofbasement walls. Such panels do not permit of high speed production andare not capable of being quickly and easily interlocked together in theerection of a house or other structure.

U.S. Pat. No. 4,457,091 discloses a hollow panel member having a widthof about one and one-half inches (11/2") and a complicated interiorformed by pultrusion, a process involving drawing long glass strands anda plastic binding material forcefully through a die under heat to formthe glass strands into a compacted glass mat bound together by theplastic material. Such a process is prohibitively slow and expensive andthe panels themselves do not provide acceptable or practical low coststructures for forming the walls and roofing of a housing system such ascontemplated by the present invention.

While modular building structures using modular building componentsformed of steel have also been proposed, such as disclosed in U.S. Pat.No. 1,958,124, such systems involve welding together of the members tomake up the components and the use of bolts or other fasteners to securesame together.. Such systems are not practical for low cost practicalhousing and the like with which the present invention is concerned.

SUMMARY OF THE INVENTION

In accordance with the present invention, the structural buildingcomponents comprise elongated thermoplastic extrusions presenting spacedinterconnecting means, preferably spaced inwardly extending interlockingmeans extending the length thereof for sliding interlocking engagementwith mating interlocking means of an adjoining mating structural member,said extrusions having at least one longitudinal web supporting theinterlocking means in spaced relation with the web having a plurality ofopenings cut therethrough inwardly of the interlocking means and spacedalong the length of the web.

According to the preferred form of the invention the openings arecircular and preferably of a uniform diameter and more preferably stillthe openings have a diameter equal to a major portion of but less thanthe spacing between the interlocking means.

Preferably the structural components of the present invention areextruded from a vinyl chloride, preferably a polyvinyl chloride,containing a reinforcing and expansion controlling agent whichpreferably is selected from one or more of mineral fibres, small glassfibers and calcium carbonate.

More particularly, the extruded structural components comprise a core ofpolyvinyl chloride Containing a reinforcing and expansion controllingagent as aforesaid and a coextruded thermoplastic skin covering surfacesthat will be exposed on assembly into a building structure.

Further, in accordance with the invention, the openings in the at leastone web of the structural component are bored out of the web immediatelyafter the component has been extruded and while it is still feeding awayfrom the extruder.

Also, according to the invention, the material removed from the web isreturned for reuse as a core extrusion material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will be understood from thefollowing detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a perspective view of a small house erected from interlockingthermoplastic structural components such as form the subject matter ofthe present invention.

FIG. 2 is a broken away perspective view illustrating a wall panelembodying the present invention seated on a concrete base ready toreceive concrete or other anchoring material to be anchored to the basethrough suitable anchor rods.

FIG. 3 is a perspective view illustrating a wall section showing a pairof wall panels interlockingly engaged with a connecting box connectorand showing the components as comprising a core having the exposedexternal surfaces thereof coated with a smooth thermoplastic skin withthe thickness of the skin being somewhat exaggerated for purposes ofillustration.

FIG. 4 is a perspective view illustrating a plurality of roof panelscorresponding to the wall panels of FIG. 3 embodying the inventionconnected by four-way box connectors according to the invention, thefour-way box connectors being available for the attachment of claddingto the upper surface of the roof and for engagement with othercomponents beneath the roofs surface.

FIG. 5 is a plan view showing a three-way box connector interlockinglyconnecting two aligned wall panels and a third wall panel at rightangles thereto.

FIG. 6 is a perspective view illustrating a corner box connectorconnecting two wall panels in right angular relation.

FIG. 7 is a perspective view illustrating a four-way box connector forconnecting four wall panels in right angular relation.

FIG. 8 is a perspective view of a slightly modified two-way boxconnector having interior locking fingers for interlocking engagementwith a mating insert.

FIG. 9 is a view similar to FIG. 8 but showing a three-way boxconnector.

FIG. 10 is a perspective view of a wall panel according to the inventionhaving a single interior web.

FIG. 11 is a perspective view of a wall panel with no interior web.

FIG. 12 is a perspective view of a box connector joiner embodying theinvention.

FIG. 13 is a perspective view taken from the underside of a sloping wallcap embodying the invention.

FIG. 14 is a perspective view of the wall cap of FIG. 13 taken from thetop side.

FIG. 15 is a diagrammatic view illustrating the manner in which thecomponents of the present invention are extruded and then drilled toproduce the openings through the webs thereof.

FIG. 16 is a cross-sectional view of the particular box connector shownbeing extruded in FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It will be understood that while only FIG. 3 illustrates the coextrudedskin on the exposed surfaces of the wall panels and the box connector,all of the panels and box connectors will have such an extruded skin andit is only components such as the box connector joiner of FIG. 12 whichwill have no exposed surfaces when assembled into a building structurethat will be extruded without any skin coating.

With reference to the drawings, FIG. 1 is a perspective view of a house1 as an example of the type of building that can be erected with thethermoplastic interlocking building components of the present inventionwhich can be assembled into walls 2 and roofing 3 with provision fordoors 4 and windows 5.

A building such as illustrated in FIG. 1 is intended to be erected on aconcrete pad 6 as illustrated in FIG. 2 which shows how the walls 2 ofthe building can be anchored to the concrete pad 6 by means of anchorrods 7 when the interior of the walls 2 are filled with concrete and thelike as illustrated by the arrow A. Suitable means such as the strip 6'may be employed to contain the concrete from spilling out fromunderneath the wall 2.

As more particularly illustrated in FIG. 3, the walls 2 are formed fromwall panels 8 interlockingly interconnected by box connectors 9, one ofwhich is illustrated in FIG. 3.

Each of the wall panels 8 in accordance with the invention disclosed incopending Canadian Application Ser. No. 2,070,079 comprises a hollowrectilinear thermoplastic extrusion having a core 10 and coextrudedouter skin 11.

The core 10 preferably comprises a vinyl chloride and, moreparticularly, a polyvinyl chloride containing a suitable reinforcing andexpansion controlling agent such as mineral or other fibers or otherknown expansion controlling agents such as a calcium carbonate.

A reinforcing agent or constituent particularly useful for structuralcomponents of the present invention which are subject to high loadingcomprises small glass fibers which when anchored in a thermoplasticmaterial such as vinyl chloride or polyvinyl chloride provide therequisite reinforcing and expansion controlling characteristics toprovide high structural strength.

A suitable material incorporating small glass fibers which can be usedin the production of these panels 8 is available under the trade-markFIBERLOC from the B. F. Goodrich Company of Akron, Ohio, such materialbeing described in detail in B.F. Goodrich's U.S. Pat. No. 4,536,360wherein very fine short glass fibers are bound within a composition ofvinyl chloride resin.

The presence of glass fibers in the PVC or other thermoplastic materialwhile providing tensile strength and expansion control to the materialcreates an extrusion problem and, if they are too large and tooconcentrated, it is not practical to extrude the material. Preferably,such fibers should be of the order of a few microns in diameter and afew millimeters in length and in concentrations not greater than andpreferably substantially less than about 35% by weight based upon thecombined glass fibers and vinyl chloride resins.

The presence of the glass fibers creates a brittleness which makes astructure produced solely from a glass fiber reinforced plastic subjectto potential fracture from impact. This potential increases withincreased concentration of glass fibers.

The problems encountered with the use of the glass fibers as thereinforcing constituent while utilizing their beneficial reinforcingqualities for high loading capacity have been resolved by coextendingwith the glass reinforced thermoplastic a smooth thermoplastic skincovering the external exposed surfaces of the panels.

The smooth plastic skin may be PVC, rigid PVC, semi-rigid PVC, ABS,polycarbonate with thermoplastics available from G.E. under thetrade-mark GELOY and NORYL.

This skin 11 serves a number of useful purposes. Because of the presenceof the glass fibers in the core or substrate 10, the substrate issomewhat brittle and its surfaces are rough and abrasive with portionsof the glass fibers projecting through the surface of the substraterendering the substrate somewhat porous and susceptible to the ingressof moisture which can adversely affect the bond between the glass fibersand the thermoplastic material.

The coextension of the thermoplastic skin covers and seals the outerexposed surfaces of the structural component against the ingress ofmoisture, thereby maintaining the integrity of the binding of the glassfibers to substrate plastic. Further, the outer skin 11 not only coversexposed glass fibers but these exposed glass fibers become embedded inthe thermoplastic material so that the external surface of the componentis totally smooth. The glass fibers in turn in becoming embedded in theouter skin lock the skin to the substrate or core 10 so that theexpansion and contraction of the outer skin is fixed to the expansionand contraction of the core which is controlled or limited by thepresence of the incorporated glass fibers which have a much smallerco-efficient of expansion than the plastic.

It will be also understood that the skin 11 can be formulated to includeagents providing impact resistance, resistance to ultraviolet radiationand the like.

The combination of the co-extruded core or substrate 10 and smooth skin11 thus enable the provision of wall panels having inherent structuralstrength and which are essentially maintenance free, impact resistantand they will be free from corrosion, rot or rusting and will beimpervious to moisture, termites and other insects.

While the use of the glass fibers provides the strength necessary forhandling high loading, where the panels will be subjected to muchlighter loading the core 10 may be formed of a vinyl chloride containingfrom about 5% to about 50% calcium carbonate and preferably about 5% to30% calcium carbonate by weight.

Alternatively, a mixture of calcium chloride and glass fibers or otherreinforcing agents such as mineral fibers may be used to meet theparticular load specifications required for the panel.

As illustrated in FIG. 3, each of the panels 8 is provided with twotransverse webs 12 which tie the opposing faces 13 of the panel togetherintermediate the edge walls 14 of the panel.

Adjacent each of the edge walls 14, the panel 8 is provided withinwardly extending oppositely registering grooves 15 with the width ofthe panel being reduced outwardly of the grooves 15 to the edge walls 14to, in effect, provide a tongue portion 16.

As the cost factor is a critical element in the ability to provideaffordable housing to the masses, it has been found that this costfactor can be significantly reduced in material costs by cutting aseries of openings 17 out of the webs 12 and edge walls 14 at spacedpoints along their length.

This cut out material can then be collected and reused in the extrusionof the core of a subsequent extrusion.

The openings 17 are preferably circular openings having a diameterslightly less than the spacing between the most adjacent point 18 of thegrooves 15.

With the openings 17 centered on the midpoint of the edge walls 14 andmidway between the panel faces 13, the openings can be cut through theedge walls 14 and also through the webs 12 without interference with thegrooves 15 which extend uninterrupted throughout the length of theextrusion.

Still with reference to FIG. 3, the panels 8 are shown interlocked withthe box connector 9 in the form of a hollow extruded rectangle havingprojecting flanges 19 terminating in inturned oppositely registeringlocking fingers 20 adapted to slidingly interlock with the grooves 15 ofthe panels 8.

The box connector 9 is extruded with a core 21 and a coextruded outerskin 22 covering the outer surfaces of the walls 23, the flanges 19 andthe locking fingers 20.

Because of the inherent strength of the configuration of the extrudedrectangular box connector 9, its core 21 may comprise a PVC resin and,for example, calcium carbonate, as the expansion controlling andreinforcing agent, although other agents including small glass fibersand mixtures of agents may be used.

It will be noted that the outer surfaces of the walls 23 of the boxconnector 9 covered by the outer skin 22 are precisely aligned with theouter surfaces of the panel faces 13 with the tongue portions 16 of thepanels being received in the space between the inturned locking fingers20 and the transverse walls or webs 24 of the box connector.

Again, the box connector is provided with a series of openings 25through the transverse walls or webs 24. Again, these openings arecircular with a diameter centered on the midpoint of the transversewalls or webs 24 of the box connector and spaced along the lengththereof with the diameters of the openings substantially equal to, butless than, the spacing between the inturned locking fingers 20 so thatthe locking fingers are not intersected during the cutting of theopenings 25.

It will be seen that the panel locking grooves 15 are covered in thesmooth coextruded skin 11 to provide a smooth surface for smooth slidinginterlocking engagement with the smooth skin coated locking fingers 20.Further, the outside faces of the tongues 16 which form the edge walls14 of the panels are coated with the smooth skin 11 and preferably thesefaces are slightly concaved to eliminate any interference with the boxconnector transverse webs or walls 24.

Again, the material cut out from the box connector walls or webs 24 canbe collected and returned to be used as material for extrudingsubsequent box connectors.

It has been found, for example, that with a wall panel width of 100millimeters between the faces 13, circular holes having a diameter of 70milliments and spaced 12.7 millimeters apart provide a significantsaving in material and cost of the vinyl extrusion product withoutsignificantly affecting the structural strength of the panel so thatwhen concrete is poured therein such as illustrated in FIG. 2 to convertthe wall panel into a permanent wall configuration the webs and edgewalls of the panels which are placed under tension exhibit adequatetensile strength tieing the panel faces 13 against outward bulging underthe concrete load.

In addition to the savings in material costs, the provisions of theopenings 17 and 25 limits thermal transfer between the outer or exposedfaces 13 of the panels 8 and the outer exposed walls 23 of the boxconnector 9. As a result the components provide increased insulationbetween the exterior and interior wall of a building such as shown inFIG. 1.

FIG. 4 illustrates an arrangement of roofing panels 26 which are showninterlocked together by four-way box connectors 27 rather than a two-waybox connector 9 as illustrated in FIG. 3 and which would be used toprovide the smooth roof formation shown in FIG. 1.

The four-way box connectors 27 provide for interlocking roof cladding tothe upper surface of the roof and for engaging or supporting otherstructures beneath the roof.

The roof panels 26 are similar to the wall panels 8 and it will beunderstood that they are extruded to provide a core and a coextrudedouter skin covering the outer surfaces thereof (the separate layers notbeing shown).

Again, depending upon the anticipated loading of the roof structure, thereinforcing agent or agents selected for the core of the roof panels 26will be appropriately selected.

For high loads the reinforcing agent preferably would include at leastsome of the fine small diameter short glass fibers.

Again, as in the case of the wall panels 8, the roof panels 26 areformed at opposite longitudinal edges with oppositely registeringinwardly extending locking grooves 28 and edge tongues 29 for slidinginterlocking engagement with the inturned locking fingers 30 carded bythe flange extensions 31 of the box connectors 27. Similar inturnedlocking fingers 30 are provided on the box connectors 27 to projectabove and below the interlocked roof panels.

The roof panels 26 have circular holes 32 cut through their edge tongues29 and webs 33 corresponding to the circular holes or openings 17 cutout from the wall panels 8. Similarly, the four-way box connectors 27have circular openings 34 cut therefrom corresponding to the openings 25in the two-way box connector.

In a roofing structure formed from the thermoplastic components, it ishighly desirable that air circulation be effected within the roofstructure. In this respect, the cutting out of the holes 32 and 34provides free air circulation laterally of the roof in addition to theair circulation with can be effected lengthwise of the elongated hollowextruded roof components.

Additionally, it will be appreciated that the provision of the openingsin the roof panels and their connecting box connectors restrict thermaltransfer from the upper roof surface to the underside of the roofthereby adding to the thermal insulation provided by the components. Itwill also be appreciated that, if desired, the roof panels andconnectors can be filled with suitable insulating material.

Despite the removal of the material resulting from the cutting of thecircular holes 32 from the roof panels the webs 33 provide the requisiteresistance to roof panel bending to sustain high roof panel loadingaugmented by the interengaging panel tongues 29 and box connectorflanges 31 and locking finger 30.

FIG. 5 is a plan view illustrating the connection of three wall panels 8into a T-formation using a three-way box connector 35. The three-way boxconnector is provided with openings 25 in three of the walls thereof sothat when material is introduced as indicated by the arrow 36 into thebox connector 35, which material may be concrete, sand or insulationmaterial, it can flow through the various openings into the wall panels.As illustrated, the leg of the T-formation is closed by an end cap Cformed to interlock with the tongue 16 and grooves 15 of one of thepanels 8 to contain all material within the external walls of the paneland box connector.

Similarly, should it be desirable to introduce insulation material intothe interlocked roof panel as illustrated in FIG. 4, such material canbe injected for distribution within the roof structure by virtue of theexistence of the cut out holes. Since the spacing between the holes ismuch less than the diameter of the holes, there will always besignificant registration between the holes or openings cut in theadjoining interlocking components.

FIG. 6 illustrates a corner box connector 37 connecting two wall panels8 together in right angular relation. Box connector 37, as before, isextruded with an appropriate core and a co-extruded outer skin and isprovided with the requisite inturned locking fingers 38 on adjacentsides and with the cut out circular openings 39 centered between theseinturned locking fingers and having diameters less than the spacingbetween the locking fingers.

FIG. 7 shows a four-way locking connector 40 for interlockinglyconnecting four wall panels 8 in right angular relation. In this case,the connector 40 has inturned locking fingers 41 at all four sides ofthe connector and circular openings cut out therefrom in all four wallsof the connector.

It will be understood again that the connector 40 is formed of areinforced core with the exposed surfaces, that is the locking fingers41 and their supporting flanges 42 coated with a smooth skin:

It will be noted that the arrangement of the openings cut out from thevarious extruded components is such that the openings are internal ofthe exterior walls of the structure being assembled therefrom when theyare slidingly interlocked with the appropriate mating components.

FIG. 10 is a perspective view illustrating a wall panel 8' correspondingto the panel 8 except that it has a shorter span with a single web 12'.Otherwise the panel is identical with panel 8 and like numbers refer tolike parts.

Similarly, FIG. 11 illustrates a still smaller wall panel 80 which maybe used at a wall corner. Panel 80 has no internal webs but otherwisehas the same interlocking features and the same cutout openings as wallpanel 8 and like numbers represent like parts.

FIG. 8 illustrates a two-way box connector 9' corresponding to boxconnector 9 but additionally having internal key ways comprising outturned locking fingers 43 for sliding interlocking engagement withmating inserts (not shown).

FIG. 9 is a perspective view of a three-way box connector 35' similar tobox connector 35 but having an internal slideway comprised by out turnedlocking fingers 44 for supporting an internal insert (not shown).

FIGS. 13 and 14 illustrate a wall cap 45 adapted to fit down over thetop of a wall formed from wall panels such as panels 8 and boxconnectors such as box connectors 9 to present a sloping support surface46 for supporting a sloping roof such as illustrated at 3 in FIG. 1.

Wall cap 45 is a hollow extrusion having a bottom wall 47 adapted torest on the upper ends of an erected wall and having down-turned flanges48 forming interconnecting means adapted to embrace opposite faces 13 ofthe wall.

Webs 49 and 50 extending upwardly from the bottom wall 47 support thesloping upper surface 46 with the web 50 being of a greater height thanthe web 49.

The wall cap 45 is provided at the lower side of the sloping wall 46with a chamber 51 which has an access slot 52 which may be closed byscreening of the like (not shown). At the opposite side, the wall cap isprovided with a closed chamber 53 and an open chamber 54.

In accordance with the invention, the bottom wall 47 and the slopingwall 46 are provided with circular openings 55 cut therethrough. Forthis particular component, the diameter of the openings, while less thanthe spacing between the flanges 48, is greater than the spacing betweenthe webs 49 and 50 so that during the cutting of the openings 55 aportion of the webs 49 and 50 are removed to provide access openings 56and 57 to the chambers 51 and 54.

Since the bottom wall 47 and the sloping upper wall 46 will not beexposed when the wall cap 45 is installed in place, these surfaces neednot be coated with a covering skin. The other exposed surfaces, however,will have a skin coextruded over the core material to provide thedesired smooth finish.

FIG. 12 is an extrusion for connecting box connectors together and, whenin place, will be totally enclosed and will have no exposed surfacesthat require coating.

As illustrated, this box connector connector 58 comprises a web 59spacing two outwardly facing channels presenting two inwardly projectinggrooves 60 of a width to receive the interlocking fingers such as thefingers 20 of two adjoining box connectors 9 when their locking fingersare in abutting relation. In this manner connector 58 will lock the boxconnector together while being totally contained within the abutting boxconnector flanges and abutting interlocking fingers..

The web 59 is provided with a plurality of circular openings 61 cuttherefrom with the diameter of the openings being substantially equal tobut slightly less than the spacing between the two channels 60.Connector 58 is preferably extruded from a polyvinyl chloride but sinceit is not subjected to significant loading the amount of reinforcingagent, if any, can be minimal. Again, because it is enclosed when inposition, no exposed surfaces requiring a skin coating are presented.

FIG. 15 is a diagrammatic illustration of the method of manufacturingthe extruded components of the present invention and illustrating theextrusion of a straight box connector 9 having a core 21 and acoextruded outer skin 22 and provided with circular openings 25 cuttherefrom.

As illustrated, thermoplastic material 62 formulated with the desiredingredients to form the core of the box connector 9 is fed from hopper63 into a suitable extrusion die (not shown) from which it is deliveredin a continuous stream having the requisite cross-sectional shape. Atthe same time, material 64 suitable for the coextruded skin is deliveredfrom hopper 65 and coextruded to cover the exposed surfaces of the boxconnector.

As the coextruded core and skin are fed continuously out of theextrusion die arrangement suitable rotary drills 66 carded by ahorizontally reciprocating carriage 67 mounted on guide 68 are utilizedto drill the holes 25.

The movement of the carriage 67 is such that it moves away from theextrusion apparatus at the same speed as the box connector extrusion isdelivered out of the extruder so that during the drilling the extrusionand the drills have no relative movement in the direction of extrusionfeed. As soon as the holes are cut and the drills retracted, they arerapidly returned rearwardly of extrusion feed to the start position tothen recommence a fresh cycle of drilling while moving at the same speedas the extrusion feed.

The drills are arranged so that when they retract they withdraw thematerial cut from the extrusion where it can be dropped unto a collectorpan 69 and delivered back by a suitable feed 70 into the core materialhopper 63.

Following extrusion and drilling, the box connector extrusion can be cutoff at the requisite lengths depending on the nature of the buildingstructure with which it is to be employed.

By using the structural components of the invention which have materialcut or removed therefrom and recycled as described, savings in the costof a building such as a house of up to 25% can be achieved furthersignificantly increasing the affordability of housing and the like forthe low income masses.

While a number of different structural components have been shown anddescribed, it will be understood that the principles of the inventionmay be employed to produce various other structural component profilesto meet the requirements for producing the shape of the buildingstructure desired. It will also be understood that variations may bemade in the details of the component structures and the arrangement ofthe material cut out may be made without departing from the spirit ofthe invention or scope of the appended claims.

I claim:
 1. An elongated hollow generally rectilinear thermoplasticstructural component for use in the erection of a thermoplastic buildingstructure, said component comprising a coextrusion of a hollow substrateof reinforced thermoplastic material having spaced substantially planarwalls held in spaced relation by transverse walls or webs and havinginterlocking means extending the length of said planar walls and asmooth protective coextruded thermoplastic skin covering the outersurfaces of said planar substrate walls, said transverse walls or webshaving material cut therefrom to provide a plurality of openings alongthe length thereof and inwardly of said interlocking means, the materialcut from said walls or webs providing material suitable for use assubstrate material in the coextrusion of a subsequent component.
 2. Anelongated thermoplastic building component as claimed in claim 11 inwhich said substrate material is a polyvinyl chloride containing areinforcing and expansion controlling agent.
 3. An elongatedthermoplastic building component as claimed in claim 2 in which saidsubstrate contains material cut out from the walls and webs ofpreviously extruded components.
 4. An elongated thermoplastic buildingcomponent as claimed in claim 2 in which said reinforcing and expansioncontrolling agent in said substrate is selected from one or more of thegroup consisting of mineral fibers, glass fibers and calcium carbonate.5. An elongated thermoplastic building component as claimed in claims 1,2 or 3 in which said component comprises a longitudinal panel and saidtransverse webs include webs which extend across between saidsubstantially planar walls and form the longitudinal edge walls of saidpanel and at least one web which defines internal compartments withinsaid panel between said panel edge walls, and said interlocking meanscomprises inwardly projecting oppositely registering grooves in saidsubstantially planar walls adjacent each of said panel edge walls andextending throughout the length of said substantially planar walls, thespacing between said substantially planar walls being reduced outwardlyof said grooves to provide a locking tongue and said openings areprovided in each of said webs.
 6. An elongated thermoplastic buildingcomponent as claimed in claims 1, 2 or 3 in which said componentcomprises a box connector in the form of an elongated hollow rectangle,two opposed walls of which are constituted by said substantially planarwalls, and two walls of which are constituted by said transverse webs.7. An elongated thermoplastic building component as claimed in claims 1,2 or 3 in which said smooth skin is selected from one of the groupconsisting of PVC, rigid PVC, semi-rigid PVC, ABS, and polycarbonate. 8.An elongated thermoplastic building component as claimed in claim 7 inwhich said substrate comprises a polyvinyl chloride containing fromabout 5 to 50% calcium carbonate.
 9. An elongated thermoplastic buildingcomponent as claimed in claim 8 characterized in that said substratecontains from about 5 to 30% calcium carbonate by weight.
 10. Anelongated thermoplastic building component as claimed in claims 1, 2 or3 in which said skin has a thickness at least of the order of about0.015 inches and said substrate has a thickness of the order of at leastabout 4 to 5 times the thickness of said skin.
 11. An elongatedthermoplastic building component as claimed in claims 1, 2 or 3 in whichthe spacing between opposing walls of each said component is of theorder of several tens of times the combined thickness of said substrateand skin.
 12. An elongated thermoplastic building component as claimedin claim 1 in which the amount of material cut from said walls or websis a substantial proportion of the total amount of material in saidcomponent prior to removal of the cut out material.
 13. An elongatedthermoplastic building component as claimed in claim 12 in which saidsubstantial proportion is of the order of up to about 25% by weight. 14.A method of manufacturing hollow rectilinear thermoplastic buildingcomponents adapted for interlocking engagement to form buildingstructures, said method comprising co-extruding said components toprovide spaced planar walls held in spaced relation by transverse websand presenting interlocking formations for interlocking engagement withmating components, salad building components being formed of substratematerial containing a reinforcing agent, while co-extruding a thinsmooth thermoplastic skin to cover the outer surfaces of said planarwalls, cutting material from said transverse walls and webs to provideopenings therethrough, recovering said material cut from said transversewalls or webs, and reusing said recovered materials as substratematerial in the coextrusion of a subsequent component.
 15. A method asclaimed in claim 14 in which said substrate material is a polyvinylchloride containing a reinforcing and expansion controlling agentselected from one or more of the group consisting of calcium carbonate,mineral fibers, and small glass fibers.
 16. A method as claimed in claim14 or 15 which said smooth thermoplastic skin is selected from one ofthe group consisting of polyvinyl chloride, rigid polyvinyl chloride,ABS and polycarbonate.